1. Technical Field
The disclosure relates to a diode array structure, and more particularly to a light emitting diode (LED) array structure, and a printing head and a printing device thereof.
2. Related Art
A photocopier, a printer, a fax machine, and a multifunction peripheral use electro-photography as a core technology for printing a document; that is, the devices generate a photographic image by changing the distribution of electrostatic charges through light with a specific wavelength.
Please refer to FIG. 1, which is a schematic view of a LED printer 100 for color printing. The LED printer 100 has photoconductive drums (110K, 110M, 110C, and 110Y, referred to in sum as 110), printing heads (120K, 120M, 120C, and 120Y, referred to in sum as 120), and toner cartridges (130K, 130M, 130C, and 130Y, referred to in sum as 130), corresponding to black, magenta, cyan, and yellow respectively. Through a power distribution mechanism, a layer of uniform charges is generated on a surface of the photoconductive drum 110. In a scan procedure before printing, an exposure procedure is required to makes pixels of a pattern in a document to be printed convert to light and shade data of the visible light. The printing head 120 has a plurality of LEDs arranged along a one-dimensional direction. When light emitted by the LEDs is irradiated onto the photoconductive drum 110, potential of an unexposed area remains unchanged, but charges of an exposed area vary due to exposure. The variation of the potential of the exposed area may absorb carbon powder which is provided by the toner cartridge 130 and carries positive and negative charges, so as to achieve an objective of printing.
To improve the printing resolution, the LEDs in the printing head 120 are arranged tightly. For example, to reach a printing resolution of 600 DPI (Dots Per Inch), an interval of 42.3 μm between the LEDs is required. However, the area of an LED is further limited, and a light emission amount of the LED is limited. Therefore, how to improve the area of the LED to raise the light emission amount of the LED is a research subject of the researchers in the art.